Method of casting patterned plastic sheets



METHOD OF CASTING PATTERNED PLASTIC SHEETS Filed April 8, 1953 INVENTORFrank E. Porter BY 5a ATToRNE s beads.

Patented Feb. 9, 1954 'METHOD 0F CASTING PATTERNED PLASTIC SHEETS FrankE. Porter, Dcnville, N. J., assig'nor to U. Chemical Corporation,Metuchen, N. J., a corporation of New Jersey Application vApril 8, 1953,Serial No. 347,555

Claims. 1

This invention relates to preparation of cast synthetic resins and,Vmore specifically to the preparation of such resins in the form ofsheets containing pattern forming additives, andthe primary object ofthe present invention is to provide a `process of eiecting a -controlledorientation of pattern forming additives of cast synthetic resin sheet.

According to this invention the pattern forming material, such as pearlessence from sh scales, metal bronze powders, pigments of `variouskinds, and dyes, both as liquid and powders, is added directly to apolymerizable liquid organic compound such as methyl methacrylateymonomer in such manner that the cast sheet -presents a beautifulpattern formed by the additives, which pattern may be readily alteredand cont-rolled by simple variations in certain steps of the operationall as will hereinafter be more fully described.

The principal novel step in the process is the incorporation in themixture of the synthetic resin to be cast and the pattern formingadditives, of amounts of resin in the form of solid spheres or beads ofselected mesh size which, in the process of casting, move in the heatedmixture until the increasing viscosity of the plastic as it setsprevents further movement of the In this movement, which may, in themolding of sheets for example, be accomplished by turning the mold to avertical plane, each bead carries with it a glob of viscous vresincontaining the pattern forming additive `which in turn carries with itto a greater -or 'less extent the contiguous resin, `producing acontrolled directional distribution of the a-dditive, which in the nalproduct forms a distinctive and reproducible pattern which may bemodified by changes in the quantity and size of the added beads; in theviscosity of the resin to be cast; in the kind and quantity of theadditives and otherwise.

The process may be carried out with the apparatus commonly used for themanufacture of plastic sheets and forms, and inthe vaccompanyingdrawings I have shown a typical mold used for molding sheets of acrylicresins.

In the said drawings:

Fig. 1 shows in section the open mold immediately after it is lled withplastic material;

Fig. 2 is a sectional `view of .the enclosed mold; and

Fig. 3 is a side elevation of themold positioned for the setting of theplastic and showing the distribution of the ingredients vof the plasticvat the beginning of the setting period.

Referring to the drawings, vl and 3 are glass plates between which theplastic sheet `is formed.

The sheets are spaced apart by a compressible gasket 2 in the -form of acontinuous ring of a shape and 4size corresponding with the plates lIand 3. The gasket 2 vis placed at `the edge of one plate as shown inFig. Al and the required amount of the heated -plastic poured `on theplate. The second plate is placed on top ofthe gasket and the clamps 4applied over the edges of the assembled plates and gasket and screweddown, care being taken to maintain the plates parallel so that themolded sheet will beof uniform thickness throughout. After filling -themold, it is placed in a controlled temperature bath for polyvmerization.

The following are `examples of the procedure followed in the commercialmanufacture of sheets in accordance with 'this invention-usingtheabovedescribed apparatus.

Example No. I

Monomeric methyl methacrylate containing `0.025% acetyl peroxide as apolymerizing catalyst and the reflective sheen material is heated `at8'?" C. until it .is a syrup with viscosity of .u, 'u, 10, Gardner-Holdtviscosimeter comparison control, at room temperature. One of theformulas Acommonly used for thissyrup is the following:

Parts Methyl methacrylate monomer 1 4490 Pearl essence Acetyl peroxide(dimethyl phthylate) catalyst 1.14

From the above syrup at room temperature a precalculated amount isremoved to produce a sheet .150" in thickness. To this `syruptransparent beads :of .acrylic resin of the desired dimensions areadded. The quantity Vof beadsin proportion to the amount of syrup andthickness of the sheet to 'be cast modiies the pattern in the resultingsheet. Beads iny the order of 5 grams per pound of methyl .methacrylateof approximately .20.mesh vsize will 4produce a pleasingmother-oi-pearlfpattern. After the beads are added, the vesselvcontaining the syrup is subjected to mechanical agitation'forvone (l)minute. rThe syrup, with the .added beads, is then poured into a castingycell such as-above described. The cell is placed directly after`closing into `a controlled temperature bath for polylmerization in avertical position.

In the drawings, the Ybeads are 'indicated at 5 and the sheen materialat 16, theshowing being, of course diagrammatic.

At the start of the polymerization immediately after the mold is placedin vertical position, the beads and sheen material are uniformlydistributed throughout the resin and the sheet, as shown at the left inFig. 3 presents no pattern When the mold is set on edge, the beads beginto move through the'action of the gravity and the sheen material isredistributed in the manner above described.

The iinished sheet contains a mother-ofpear pattern which, while notmade up of like areas of geometrica-Hy identical design, is of agenerally similar appearance throughout the sheet and reproducible fromsheet to sheet to such an extent that if a number of sheets be cut intosmall pieces of identical size, it would be impossible to tell from theappearance of the pieceswhich sheets they came from.

Example No. 2

The procedure followed is the same as in Example No. l except thatviscosity of syrup is increased to Z-I-l, Gardner-Boldt viscosimetertube control. The pattern in the resultant sheet is of smaller design,with individual iigures approximately 1% to 1 in size over the entirearea.

The control of the design in the finished sheet as to size and intensityof striation, is a function of the pouring viscosity of base syntheticresin liquid and the temperature of the polymerization unit. Theviscosity of the casting base is adjusted to ball size to controlreproducible pattern. For light caliper sheeting, a spheroid ball of to30 mesh is added to the base liquid with a Gardner-Holdt controlledviscosity of "u, 17, w cold. For calipers from 250/ to 500/ inclusive aviscosity of 2t-l- 1 e4-2, Gardner-Holdt is used with balls of 10 to 40mesh size. The sheetsare cast in a waterbath in a vertical position andthe design is created by the shifting or falling movement of thespheroid polymer through the base synthetic resin liquid containing thematerial producing the reflective sheen. This shift caused by thefalling spheres creates a new stage of orientation in the reilectivesheen material thereby creating the design. The shape and size of thedesign is a direct function of the viscosity of the base synthetic resinliquid and the size of the beads. For small design the viscosity isincreased to reduce falling inertia of balls and for large design, theviscosity is reduced to increase falling speed of spheres. The patternsareV directly reproducible in area as long as the same size spheroidsynthetic resin bead is used. The pattern is throughout the entirethickness of the sheet and is not limited to one side. No furtherprocessing of cast sheeting is required after material is loaded tocasting cells, designing then becomes a routine and not a manualfunction of the procedure.

In the foregoing examples I have described the vprocedure followed inmaking sheets having patterns formed of pearl essence added to thetransparent resin. The patterns formed are generally similar inappearance to so-called motherof-pearl with the sheen materialapparently somewhat more concentrated in limited areas dispersedthroughout the area of the sheet, the limited areas being in the form ofirregular paths extending generally in the same direction, whichdirection was downward during the period that the material was settingin the molding cell. The length and width of these areas varies with theviscosity ofthe resin when placed in the cell and the size of the addedbeads.

Mother-of-pearl patterns may be formed in sheets of any color by addingto the resin a dye in liquid form which gives a color to the sheetwithout rendering it opaque. In the finished sheet the dye appears tohave a greater concentration in the limited areas where the sheenmaterial appears to be more concentrated, but this may be due to thegreater opacity of the sheet in these areas. Instead of using sheenmaterial for forming the patterns, metallic powders in the form used'for making paints, such as bronze powder or aluminum powder, may beemployed. These powders are apparently re-oriented in the mass by thedownward movement of the beads in the same manner as the pearl essence.Pigments other than metallic powders may also be employed and alsoliquid dyes may be employed without sheen material.

The beads should preferably be formed of resin of the same compositionas the sheet material, so that the beads, to the extent that they aremelted during the setting of the resin, will blend with and form part ofthe sheet.

When the pearl essence or other reective sheen material is added to thesemi-liquid resin before casting without the addition of the beads, itis impossible to effect a distribution of the material throughout theresin in such manner as to produce a controlled and reproducible patternno matter how carefully the agitation of the mixture of semi-liquidplastic and the reflective sheen material is controlled, and no matterhow exactly such agitation is reproduced the distribution of the sheenmaterial will not be reproduced and the resulting pattern is entirelyunpredictable. Apparently the beads in some manner control thedistribution of the sheen material, and if beads in the same number andsize be added to the same liquid plastic and the viscosity of theplastic and other conditions of the casting process be carefullyreproduced, the resulting pattern will be substantially the same in theseparately cast sheets. Also, as pointed out above, the resultingpattern may be controlled by varying the size and number of the beadsand the viscosity of the semi-liquid .plastic at the time the beads areadded to the plastic and the mixture agitated as described.

In the foregoing specification I have described in detail my improvedprocess as carried out in the commercial manufacture of sheets of thecharacter described, but it is to be understood that my invention is notlimited to the details of the procedure herein described, but the samemay be varied within the scope of the appended claims.

I claim:

l. The method of making molded articles which consists in adding to amolding composition while in a liquid state a quantity of patternformingmaterial, also adding to said liquid composition discrete particles ofsolid material of such weight and bulk as to sink by gravity in ing tosaid liquid material discrete solid substantially spherical particles ofa composition to blend with liquid and of such Weight and bulk as tosink by gravity in such molding composition, placing the mold inposition for such particles to move downwardly, subjecting the mold toconditions to cause the Composition to solidify, and controlling thesolidii'lcation of the composition so that it is not solidified untilafter the particles have sunk a substantial distance in the composition.

3. The method of making molded sheets Which consists in adding to themolding material While in a liquid condition a quantity ofpattern-forming material of comminuted form, also adding to said liquidmaterial a plurality of transparent beads of a composition and to be atleast partially melted at the temperature of the liquid material and ofsuch weight and bulk as to sink by gravity in said molding composition,placing the mixture in a mold, positioning the mold in a vertical plane,subjecting the mold to conditions to cause the composition to solidify,and controlling the solidication of the liquid composition so that it isnot solidified until after the beads have sunk a substantial distance inthe composition.

4. The process of claim 1 wherein the molded articles are sheets and themold is set on edge While the composition is solidifying.

5. The method of claim 2 wherein the molded articles are sheets and themolds are set on edge during the setting period.

FRANK E. PORTER.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,168,331 Fields Aug. 8, 1939 2,265,226 Clewell Dec. 9, 19412,480,750 Leary Aug. 30, 1949

